Yes, a sponsored walk is a good idea too. We did one from our dog training club last year, we had 51 dogs show up and we also made money by providing a sandwich/drinks stand halfway round.
Another sure-fire money maker is dog racing - all you need is an enclosed field, a couple of posts and some marker tapes, and maybe a small prize for the winners. We do it with small, medium and large groups, each dog runs separately down a straight course chasing after the owner and is timed from start to finish line. But prepare to spend a whole day at it! At two tries each, it adds up to a whole lot of time. We always get a few small dogs, quite a lot of mediums, and a huge class of large dogs.